The present invention relates to a temperature sensor control apparatus which energizes a temperature sensor whose electric resistance varies in accordance with a temperature.
Heretofore, there is used a temperature sensor control apparatus arranged to energize a temperature sensor whose resistance varies in accordance with a temperature, at a temperature detection of a measured fluid such as exhaust gas by using the temperature sensor.
The temperature sensor control apparatus includes reference resistance elements connected in series with the temperature sensor. The temperature sensor control apparatus senses a voltage value divided by the resistances with respect to an impressed voltage (that is, an electric potential of a connection point between the temperature sensor and the reference resistance element), and determines a resistance value of the temperature sensor in accordance with the electric potential of the connection point. This temperature sensor control apparatus determines the temperature based on temperature-resistance characteristic of the temperature sensor.
The temperature sensor has a characteristic having a region in which an amount of variation of the resistance value is small with respect to an amount of variation of the temperature, and a region in which an amount of variation of the resistance value is increased with respect to an amount of variation of the temperature. Accordingly, the amount of variation of the resistance value is not constant in all the temperature region. In the region in which the amount of the variation in the resistance value is small with respect to the amount of the variation in the temperature, the sensed voltage value divided by the resistance tends to vary for the noise, so that the detection error tends to occur in this region.
For solving the above mentioned problem, a published Japanese patent application No. H5-45231 and a published Japanese patent application No. 2002-310807 disclose temperature sensor control apparatuses devised to decrease the resistance value of the reference resistance elements relatively with respect to the temperature sensor by switching the reference resistance elements connected in series with the temperature sensor. Accordingly, it is possible to decrease the influence of the noise.